1. Field of the Invention
This disclosure relates generally to a derailment detector and method and, particularly, to a derailment detector and a method for detecting and signaling a derailment condition in a railway vehicle.
2. Description of Related Art
Derailments in the rail industry often result in substantial damage to railway vehicles and tracks, as well as a significant loss in revenue to operators due to the derailed railway vehicle and/or the track being out of operation. The serious consequences resulting from the derailment of railway vehicles have led to the development of derailment detectors adapted to detect a derailment of the railway vehicle and immediately apply the appropriate corrective measure. Conventional derailment detectors typically activate a full emergency brake function upon derailment detection. While the ultimate goal in a derailment situation is to stop the railway vehicle as soon as possible, certain situations, such as derailment in a tunnel, on a bridge, or during a false activation, demand an alternative means of initiating the stopping procedure.
In particular, systems based on an inertia sensor are known where, upon activation of the inertia sensor, the pressure inside the brake pipe is quickly released to cause the emergency brake application of the railway vehicle that acts on all cars in the composition. Within the prior art, U.S. Pat. No. 5,188,038 to Shanley is directed to a railroad car derailment safety device that activates the air-brake system immediately upon detection of a derailment condition. The device includes a bar extension projecting from a bottom portion of each car to a position slightly above the rail. Upon railroad car derailment, the bar contacts the rail, causing a trip valve in the air-brake line to open and release the pressure in the brake line, thereby applying the brakes. Derailment detectors of this type function as emergency brace valves.
However, conventional derailment detectors have a major drawback in that full braking force is applied to stop the railway vehicle as quickly as possible in a shortest possible distance. While the ultimate goal is to safely bring the railway vehicle to a complete stop, emergency brake application upon derailment detection can result in the stopping of the railway vehicle in an undesirable location, such as inside a tunnel or on a bridge. This complicates the effort to repair the derailed vehicle and/or the track, and resume normal railway travel.
Certain efforts have been made to develop derailment detectors which alert the operator of the railway vehicle that a derailment condition has occurred. For example, U.S. Pat. No. 3,994,459 to Miller et al. is directed to a railway vehicle derailment detection system having an acceleration responsive device that, in response to the changes in vertical acceleration of the vehicle as a result of the derailment, sends a radio signal installed in the engine to provide a visual or an audio alert to the operator. The acceleration responsive device is embodied as a piezo-electric element that is operative for transmitting an electrical signal when the sensor element is activated as a result of vehicle derailment. The system described in this patent does not include a pneumatic means for providing an indication to the operator that a derailment situation arose.